Chronic angina pectoris is a very common disease in the United States. Currently, the most common methods of reperfusing ischemic myocardium are cardiac arterial bypass graft (CABG) and percutaneous transluminal coronary angioplasty (PTCA) operations, with 330,000 and 500,000 such procedures performed every year in the United States. Both techniques restore blood flow to the ischemic myocardium by bypassing or removing the atherosclerotic lesions which obstruct blood flow. However, despite advances in treatment techniques, there is a large group of patients who cannot undergo CABG or PTCA due to severe diffuse coronary atherosclerotic disease.
The concept of supplying blood to a myocardium devoid of the natural arterial network is not new. It was discovered many years ago that reptiles have no major coronary arteries and that their hearts are nourished by channels that supply blood directly from the heart chambers into the myocardium.
By creating such channels in ischemic human myocardium, it is possible to bring arterial blood, and therefor oxygen, directly into the deep endocardial layer of the heart muscle. Several investigators have attempted to duplicate the reptilian system in human hearts with techniques that ranged from the Vineberg procedure (implanting the left internal mammary artery into the myocardium) to the making of myocardial channels through needle acupuncture. These attempts resulted in temporary increases in myocardial protection and perfusion due to blood flow through the channels but were eventually unsuccessful as the channels quickly closed as a result of the mechanical trauma associated with these procedures. These investigations nevertheless proved that transmyocardial revascularization (TMR) was capable of creating direct blood pathways from the ventricle into the myocardium. They also demonstrated that long term success of TMR depended upon the method used to create the transmural channels.
A high power pulsed CO.sub.2 laser can create small diameter (.ltoreq.1 mm) transmyocardial channels in less than 100 milliseconds. The laser energy vaporizes myocardial tissue along its path before being stopped by the blood present in the ventricle. This vaporization process is so fast that it does not cause thermal or mechanical damage to the surrounding tissue, thereby creating virtually char-free channels of long term patency. More specifically, the epicardial channel entry site quickly seals off under the finger pressure of the surgeon while the remaining section of the channel remains open and permits oxygenated blood flow directly into the ischemic myocardium.
There are three principal surgical approaches potentially available for TMR, open chest surgery, minimally invasive surgery and the percutaneous approach. In an open chest TMR procedure, the heart is exposed by a cardiovascular surgeon typically by a left thoracotomy. The procedure is performed epicardially (from outside the heart into the left ventricle) on the beating heart. Typically 20 to 30 channels are formed in the ischemic regions of the left ventricle. A minimally invasive TMR procedure is accomplished by using video assisted thoracoscopic surgery. The surgeon makes four incisions between the ribs, two for endoscopic instruments, one for the thoracoscope (telescope/monitoring system) and one for the laser handpiece. The pericardium is removed from the region to be treated and the channels are then formed in the left ventricle. A percutaneous myocardial revascularization (PMR) system would be used by an interventional cardiologist in a cardiac catheterization laboratory. This interventional cardiologist would access the heart through an artery and advance a catheter based PMR delivery system through the aorta and into the left ventricle. Once the catheter tip entered the ventricle, it would be guided to the ischemic regions of the endocardial surface to create channels that would pass partially through the wall of the heart.
A basic factor which must be addressed in developing a percutaneous system is the location of the catheter tip. The three dimensional location of the of the device and subsequent location of the channels formed is critical so that the channels are located in the ischemic regions at properly spaced intervals. A feature of a percutaneous myocardial revascularization system (PMR) is determining the location of the tip of the catheter and the subsequent location of the channel formed. The channels should be formed in the ischemic region of the left ventricle. Spacing of the channels at 1 cm intervals prevents creating multiple channels in one location and potentially perforating the outer wall of the ventricle causing tamponade. Spacing of the channels provides a network of channels for even reperfusion of the ischemic region.
Mapping of the heart can be accomplished by several techniques. Fluoroscopic X-ray will produce a two dimensional view (see U.S. Pat. Nos. 5,558,091 and 5,568,809) which will not provide a precise location of the catheter tip. Electromagnetic sensors could be utilized; however, additional equipment would be required to determine the location. Ultrasound trans-esophogeal echocardiogram (TEE) provides a view of a channel but it would not provide a view of multiple channels simultaneously.
In U.S. Pat. No. 5,730,741, a spiral member is shown which can be used to map the inside of an organ, but the treatment catheter is constrained to follow the spirals of the spiral member resulting in a loss of power as well as increased difficulty in guiding the catheter along the spiral configuration. Moreover, this configuration can cause a change in the modality of the transmitted laser beam and serious heating of the optical fiber itself. Also, the tip of the catheter is constrained to be positioned only where the spiral member is located within the organ.